The present invention relates to an ion implanter, and more specifically to an ion implanter having an improved specimen chamber.
The manufacture of semiconductur elements includes a step for homogeneously introducing impurities into a wafer, and the introduction of impurities is carried out by, for example, an ion implantation method which is performed under highly-evacuated conditions.
If electrical scanning by an ion beam such as used for the conventional low-current ion implanter is applied to a high-current ion implanter to effect the above-mentioned ion implantation, the secondary electrons for neutralizing the ion space charged which prevents the divergence of the ion beam are absorbed by the deflecting electrodes which are used for the electrical scanning. Therefore, the ion beam diverges due to its own space charge, and makes it difficult to perform the scanning. For the above-mentioned reasons, high-current ion implantation is usually carried out by holding the ion beam stationary and mechanically scanning the wafer in two dimensions to homogeneously implant ions.
FIG. 1 illustrates a rotary disc system employed for mechanically scanning specimens 2 in the form of wafers and the like mounted on the surface of a disc 1 which is moved in rectilinear fashion in one direction while it is being rotated. This arrangement, howevere, presents the following problems:
(1) It is difficult to introduce the rotating and rectilinearly-moving disc from the open air into a vacuum chamber while maintaining an air-tight seal.
(2) It is difficult to lubricate the mechanical portions for transmitting motion to the disc or to lubricate the straight guide portions thereof.
(3) For the reason mentioned in (2) above, it is difficult to smoothly transmit and guide the motion to the disc.
(4) For the reason mentioned in (2) above, the engaging and sliding portions tend to become worn to a marked extent, and the wafer surfaces and vacuum chamber are contaminated by the dust of abrasion resulting from such wear.
(5) For the reasons mentioned in (2) to (4) above, it is very difficult to maintain precision of operation and to perform maintenance on the system.